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Best binoviewer for Meade 127mm APO ? Optic path?

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#1 cosurgi

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Posted 13 November 2011 - 04:44 AM

Hi,

I am trying to figure out what is the best binoviewer for Meade 127mm APO. I have found
- "TeleVue Bino Vue with new 2x aplifier"
- "Baader Planetarium Binokular Maxbright"

From what I've read on reviews those seem to be the best contenders? I can afford the more expensive TeleVue - is that the best one?

Second question - do you know what is the optic path in Meade 127mm APO - question is - is it going to be possible to use binoviewer without 2x barlow?

best regards and thanks for your help!

#2 cosurgi

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Posted 13 November 2011 - 07:49 AM

Another question - have you seen anywhere 2" binoviewer?

#3 MikeBOKC

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Posted 13 November 2011 - 09:26 AM

Those two are usually listed along with the Denks as the cream of the binoviewer crop. Hard to go wrong with either.

As for two inch binoviewers, I believe Siebert is the only maker out there. Which tells me something . . . no real need for 2 inches. Plus, you are already tinkering with balance issues when you add any binoviewer and paired eyepieces to a scope. I would think a two incher would be a real balance nightmare.

Finally, someone can correct me if I am wrong here, but I believe you need to use the OCS with just about any binoviewers on refractors that are not made and advertised as BV ready/compatible.

#4 bgavin

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Posted 13 November 2011 - 10:07 AM

OP, accurately measure the amount of back focus in your scope.
My AT90EDT measures 160mm from the rear of the focuser.
My focuser travel is 120mm, so the focal plane is 40mm farther back.

The diagonal and the binoviewer unit will consume this distance.
Assume a Baader T2-Maxbright diagonal with a 54mm light path.
Add in the Siebert Black Night binoviewer with 100mm light path.

160-100-54=6mm left to locate the focal plane in the eye piece.
This is probably not enough, so a modest OCA (1.25x") is needed to lengthen the light path.

The eye piece focal plane location varies by make and model, and is not in a constant location for all EP.

If you use a conventional diagonal, it will have a longer light path, making an OCA a certainty.

#5 cosurgi

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Posted 13 November 2011 - 11:54 AM

Thanks for help. I don't have that Meade 127mm APO yet :) I'm preparing the purchase along with binoviewer, so this is why I don't know how much optics path is left for use by bino.

Thanks for help with calculating this. I'll check this once I get that Meade :)_

By OCA you mean a barlow? It seems that both binos are equipped with 2x barlow by default.

Those two are usually listed along with the Denks as the cream of the binoviewer crop. Hard to go wrong with either.

This is quite surprising, because Baader costs 250 EUR, while TeleVue costs 1050 EUR! (at astroshop.pl) If those two are the best, then maybe it's not worth paying extra 750 EUR for a unnoticeable difference in quality?

Maybe TeleVue is from US, while Baader is European? And this is why imported TeleVue is so much more expensive?

I expected some bigger difference in image quality.


#6 Tamiji Homma

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Posted 13 November 2011 - 12:41 PM

Hi Cosurgi,

The biggest difference between Baader Maxbright Binoviewer and Televue Bino Vue is clear aperture size. I think Maxbright is 23mm, Bino Vue is 27mm, full 1.25" eyepiece aperture.

If your main interest is to observe at high power (planet/lunar for example), 23mm clear aperture is more than enough. If you are looking for the widest TFOV (with 1.25" eyepiece) possible then Bino Vue wins over Maxbright.

There is a big brother of Baader Maxbright, Baader MarkV binoviewer. I think MarkV is one step up from Bino Vue and DenkII. I've been using all three binoviewers for different purpose. They are all excellent binoviewers.

Regarding binoviewer lightpath length, I think Baader binoviewers have the best possibility to reach focus to infinity without OCA (or Barlow lens), thank to T2 system and prism diagonal, Baader binoviewer gives you shorter lightpath length than others.

I don't know how much backfocus distance Meade 127 f/7.5 has but I certainly look for the information if you are planning to use with binoviewer. It is very good idea to know upfront to avoid headaches :)

I've learned hard way.

I have several refractors, not particularly advertised as binoviewer friendly scope but they come to focus to infinity without OCA (or Barlow lens).

Here is an example, TMB 130SS f/7, Bino Vue/T2 prism star diagonal, Radian 18. I have 47mm left to go.

Posted Image

This thread on Eyepiece Forum may be interesting to you as well.

Master Eyepiece Distance Chart

Eyepiece field stop position is also important part of this equation, in terms of coming to focus to infinity.

Tammy

#7 bgavin

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Posted 13 November 2011 - 01:28 PM

How interesting!
Doing the math, the BV has a published optical path of 127mm.
The T2 diagonal path is 54mm.
With "47mm left", the focuser is extended 63mm.

127 + 54 + 63 = 244mm / 9.6" focal plane distance.

I saw an old post by Markus Ludes about modern refractors needing 6" back focus to accommodate BV and imaging.
I can see why your TMB-130SS can get away without an OCA.

Nice!

#8 Tamiji Homma

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Posted 13 November 2011 - 02:13 PM

Here is photo with Televue Plossl 32mm to measure backfocus of TMB 130SS.

TMB 130SS backfocus is about 248mm (255mm - 0.25 * 25.4mm)

0.25 * 25.4 is where Televue Plossl field stop is located from shoulder of the eyepiece (Televue eyepiece spec F column).

Posted Image

Takahashi TSA 102S has about 17mm to go with the same binoviewer setup without OCA.

Tammy

#9 bgavin

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Posted 13 November 2011 - 03:10 PM

Thanks!
This confirms my math was correct. I only missed by 4mm... :jump:
When my 2" extension tube arrives, I will use your method in the photo to fine tune my AT90EDT measurement.

I don't know how much backfocus distance Meade 127 f/7.5 has but I certainly look for the information if you are planning to use with binoviewer. It is very good idea to know upfront to avoid headaches

I've learned hard way.


A picture is worth 1,000 words.. the OP can user your technique before wasting much $$$.
Especially when buying New.. hard to recover from a mistake.

#10 cosurgi

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Posted 13 November 2011 - 04:06 PM

Thanks a lot!

Posted Image

Meade 127mm APO, has FL=952.5mm. While in specification I find that tube length is 850mm, and tube diameter is 155mm. Based on photos I estimate roughly that the triplet is pushed inside by about 20mm. So in total maybe I have 80mm room.
However, on this picture I don't know where actually that tube ends, and where those extra 80mm start.

I tried to measure this based on photos:

Posted Image

EDIT: well.. now I think that my calculations are wrong. Though no idea what would be correct.

But I think that I can safely assume that I will need 2x barlow. And if not - it will be a pure luck.

I've found that Tevevue bino lightpath is 130mm, it's in "details + dimensions" on page http://www.telescope...ercorrector.cfm

But I can't find what is the lighpath of Baader Mark V bino. (you didn't post it above, right? I only see lightpath for "normal" Baader Maxbright bino as 54mm).

#11 bgavin

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Posted 13 November 2011 - 05:15 PM

For starters, refractors come to focus behind (outside) the tube assembly.
The 952mm focal length extends several cm beyond the rear of the tube assembly.

If you have not yet made your purchase, and because you are asking the above questions, I suggest holding off while you learn more.
This is not meant to be insulting.. just helpful advice to make the best purchase.

The above model has little specs available on the Meade site, nor elsewhere.
Unless Meade is the only scope available, I'd look into better brands.

Please read the last few posts of this thread.
The posts are very educational about glass types, especially the FCD1 type used in the Meade scope.

Check out the various Astro-Tech, TMB, Explore-Scientific refractors on our sponsor's site.
If $$ is not a problem, skip right to the Takahashis or Televues :grin:

#12 cosurgi

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Posted 13 November 2011 - 06:10 PM

Actually I already ordered that Meade 127mm APO. Though I am holding off with ordering binoviewer. First I'll wait for that Meade to arrive, get used to it. Then get a bino.

And yes - I never used a bino. And this Meade 127mm APO is my first bigger purchase. Previously I used for years MTO11CA 1000mm :)

But I have spend lots of time (years!) to select this particular refractor. And I've read countless number of threads (can't remember them all now :). So I prefer to skip this part "what refractor to buy?". $$ is a total limit about 7000 USD (refractor, mount, eyepieces & bino) I see that any bigger refractor is actually twice more expensive, and I don't think I can afford this now. BTW, I'm paying about 1900 USD for this Meade 127mm APO. Also I suffer a back-pain problem, and I really cannot use refractor heavier than 10kg. So This Meade is actually maximum of my weight-carry capabilities, not $$ capabilities.

Of course you are not insulting me. I know that I know very little about binos!

You are saying that Baaders usually have shorter lightpath. So what is the lightpath of MarkV ?

My reseller said that it can be possible to get those MarkV.

best regards, and again thanks for all your help!

#13 Tamiji Homma

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Posted 13 November 2011 - 07:03 PM

I measured various backfocus requirement in the past. I think this diagram would help you.

The number (in millimeter) in parenthesis is distance from end of OTA when it focuses to infinity. You can derive MarkV lightpath length (with/without 1.25x GPC, BARCON). The number not in parenthesis is distance for indoor target. The diagonal is Baader Prism Star diagonal. BARCON is Astro Physics Barlow lens, Astro Physics AP16T is T-thread 2" adapter. Quick Changer is Baader's adapter to connect MarkV and male T-thread diagonal/AP16T.

Posted Image

Tammy

#14 cosurgi

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Posted 14 November 2011 - 03:12 AM

From this I see that MarkV lightpath is 147-22=125mm.

I think in following way: when MarkV is inserted without any path correction instruments it is 22mm away from focuser. When Panoptic 24 is inserted without any correcting instruments it is 147mm away.

#15 mindburner

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Posted 28 December 2011 - 02:58 PM

I have a Meade 127 and WO binoviewers. The views are superb. Although I cannot use the 2 inch diagonal and achieve focus. I use them without the diagonal. A 1.25 diagonal would probably fix the issue

#16 cosurgi

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Posted 16 February 2012 - 02:36 PM

I have thrilling news:

The ES 127mm Carbon OTA just arrived!

It took two months, since I ordered, and in meantime I changed my order from Meade to Explore Scientific :)

Also - I have ordered Binoviewer Baader Planetarium Mark V. It should arrive in few weeks. Now I am curious if I will need that 1.25x barlow in this OTA or not. So - to measuring lightpath.

So here I need your help.

Is that a correct way to measure lightpath: I point OTA at some lightsource and without any eyepieces find where the light focuses then I measure the distance from this focus point to where the extender ends?

And then according to previous calculations (two posts above) - if it is longer than 125mm, then I don't need 1.25x barlow?

That's my OTA! Lo and behold :)

http://explorescient...arbonfiber.html

Posted Image

#17 MrGrytt

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Posted 17 February 2012 - 06:49 AM

Also - I have ordered Binoviewer Baader Planetarium Mark V. It should arrive in few weeks. Now I am curious if I will need that 1.25x barlow in this OTA or not. So - to measuring lightpath.

So here I need your help.

Is that a correct way to measure lightpath: I point OTA at some lightsource and without any eyepieces find where the light focuses then I measure the distance from this focus point to where the extender ends?

And then according to previous calculations (two posts above) - if it is longer than 125mm, then I don't need 1.25x barlow?


What you need to measure is the amount of "backfocus" that is built into the scope.
Astro-Physics scopes normally have around 165mm of backfocus and that just barely gets you by with the Baader prism diagonal that is supplied with the Mark V bino-viewer with the 1.25x corrector.

The best way to measure the backfocus, which is the distance from the back of the focuser/adapter to the focal plane, is to aim the scope at a bright light source (the moon is great for this), hold a piece of white paper behind the open focuser and find the point at which the object comes to sharp focus. Measure that distance and you'll know the amount of backfocus built into the scope.

I actually made a special tool for precisely making that measurement that makes it a lot easier than holding a piece of paper. I also will never understand why all manufacturers don't specify the exact amount of backfocus built into their scopes.

Harvey

Attached Files



#18 EdZ

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Posted 17 February 2012 - 07:00 AM

Nice tool! I could have used that 20-30 times.

edz

#19 MrGrytt

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Posted 17 February 2012 - 07:12 AM

Thanks. I have found it to be very useful.

Harvey

#20 Live_Steam_Mad

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Posted 17 June 2012 - 03:44 PM

@cosurgi Hi, what is the Star Test like with your new ES 127mm APO ?

Test on 2nd magnitude star (left most star in the main 6 star pattern of Ursa Major if I remember right) and compare if possible to the pictures in Dick Suiter's Star Testing book.
I'd be interested to see how good the Star Test is. I am about to Star Test my new Meade StarNavigator 102 shortly (2 of them, one for a local friend also, whose LX90 already star tests very well).
Cheers,

Alistair G.

#21 Alex Gastélum

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Posted 03 January 2013 - 05:07 PM

I have the ES 127 apo and thinking on getting the Baader maxbright binos






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